Is there a use for a VTVM today?

N

N8Nagel

AK Subscriber
Subscriber
I already have a Simpson 260-8P as well as two Flukes and a couple other cheap meters.

Today I saw a Heath VTVM in a thrift store, was marked $15 but I think it might have been 50% off. Movement was marked as "made by Simpson Electric"

Should I go back and get it or is it pretty much a curiosity at this point?
 
Need analog to watch the meter move instead of waiting for an update, sometimes. There are uses but DMM is much more commonly used.
 
Ya know,sometimes working on classic equipment using classic test gear is just so cool:)
 
OK, interested - how do you use it, and why would it be better/more suitable than a Fluke or Simpson?
 
They're stellar when you need to look for a peak or a null in something. Digitals are quite simply crap for that task. Scrolling numbers just won't be as easy to id as a needle movement.

Depending on the circuit, a standard analog might load it down too much. A Simpson 260 is 20k/volt on DC and I think 5k/volt on AC. Most VTVM's are 10 megohm on DC, maybe only 1 megohm on AC. The frequency response also tends to be wider with a VTVM. I usually use mine for tuner alignments. That wants very low loading, and you're adjusting for a peak most of the time. FM you adjust for a zero, but you can very handily set "zero" to be the middle of the scale so its very easy to land it there.

I have one, I use it once in a while. Its great for certain things, and sometimes just having an additional meter available. For that price I'd pick it up.
 
gadget73 said:
They're stellar when you need to look for a peak or a null in something. Digitals are quite simply crap for that task. Scrolling numbers just won't be as easy to id as a needle movement.

Depending on the circuit, a standard analog might load it down too much. A Simpson 260 is 20k/volt on DC and I think 5k/volt on AC. Most VTVM's are 10 megohm on DC, maybe only 1 megohm on AC. The frequency response also tends to be wider with a VTVM. I usually use mine for tuner alignments. That wants very low loading, and you're adjusting for a peak most of the time. FM you adjust for a zero, but you can very handily set "zero" to be the middle of the scale so its very easy to land it there.

I have one, I use it once in a while. Its great for certain things, and sometimes just having an additional meter available. For that price I'd pick it up.
Click to expand...

hrballenger said:
I like using a VTVM for head alignment on RTR and Cassette machines.
Click to expand...

+1 for both of these comments - This is exactly how I use my Simpson 260 - Chris
 
I would too. Sometimes the DMM doesn't catch the actual up and down voltage changes in real time.
 
N8Nagel said:
OK, interested - how do you use it, and why would it be better/more suitable than a Fluke or Simpson?
Click to expand...

Gadget73 said it much better than I could've:

"They're stellar when you need to look for a peak or a null in something. Digitals are quite simply crap for that task. Scrolling numbers just won't be as easy to id as a needle movement.

Depending on the circuit, a standard analog might load it down too much. A Simpson 260 is 20k/volt on DC and I think 5k/volt on AC. Most VTVM's are 10 megohm on DC, maybe only 1 megohm on AC. The frequency response also tends to be wider with a VTVM. I usually use mine for tuner alignments. That wants very low loading, and you're adjusting for a peak most of the time. FM you adjust for a zero, but you can very handily set "zero" to be the middle of the scale so its very easy to land it there. "

Hurley
 
The reason to use one has been explained perfectly well but make sure to use an isolation transformer with it or you have a chance of sparks and damage if not used with one.
 
I have an autorange FETVM (actually opamp) analog meter. When I had a VTVM it was weird why it had a +/- setting but eventually made sense. The FETVM obsoletes that selection by having an LED that turns on when the probes are swapped (and automatically reversing input probes, just like DMMs with a negative symbol).

I think the input impedance of the FETVM is the same as the VTVM at 10M ohm for most ranges (3V and up) but the 300mV range is only 1M. About the only thing that the VTVM could do that the FETVM could not was center the meter (I'd have to settle for watching the LED and point at 0V) and it had a Rx1M range. I will have to use my 20M or 2G range on one of my DMMs to check those resistors...

Also that VTVM had "reverse ohms" where infinite ohms was full scale. The FETVM I have works like most VOMs for resistance - full scale is 0 ohms.
 
OK OK... if I get out of work at a reasonable hour today I will see if it's still there... I mean for $7.50 if I'll use it once it'll pay for itself
 
The ohm scale on my RCA is the same as my Simpson 260, zero ohms to the right, infinite to the left. I have seen a backwards one somewhere, but I couldn't tell you where. Getting used to setting zero and infinite needle positions takes a little getting used to though. I changed the pots in mine out to 10 turn, it makes that a much less fussy job. Also the original pots were dying anyway. The only time the 10 turns kind of suck is when you want to center scale zero it. Lots of turning involved.
 
It would require a constantly powered meters to have the "reverse" ohms so likely only going to see this in VTVM and FETVM (and implicitly, DMM... when was the last time you saw a DMM where it was zero when you had infinite ohms? no?).

I'm not sure why one would need a 10 turn for the ohms adjust? Most of the "unpowered" passive ohmmeters (i.e. VOMs that don't have constantly running power sources) have not been too hard to zero. Dirty probes, however, can make it tough.

BTW, the FETVM I have does not have zeroing knobs...it self calibrates just like a DMM. The VTVM did, just like my regular VOMs; it had two zeroing knobs for both ends of the scale (Center/left zero for all scales, and right infinity for ohms).
 
I have one ...rarely use it, but for what they cost used, it's not a bad idea to own one, they come in handy from time to time as others have mentioned here.
 
audiodummy said:
I'm not sure why one would need a 10 turn for the ohms adjust?
Click to expand...
I used them for the ohms and zero adjust. The originals were in bad shape and it had a lot of problems with drifting as it warmed up. New single turn pots may have fixed it just as effectively, but I had the 10 turns salvaged from some other piece of gear and no other use for them. It doesn't have drift problems anymore either.
 
Ah yes, the VTVM indeed drifted (due to warmup time, past the heater warmup). But strange that a pot would drift unless it itself actually warms up over time for whatever reason. Regular VOMs the drift seems marginal if at all, though re-zeroing is frequently expected hence it's on the front panel instead of being a trimpot.
 
You must log in or register to reply here.

Similar threads

N
Simpson users - D cell replacement?
2 3
Replies
59
Views
1K
audiodummy
audiodummy
N
Best approach for dormant receiver...
2
Replies
33
Views
921
N8Nagel
N
Jcricket
I scored today, I think
2
Replies
34
Views
2K
Scuzzer
Scuzzer
Montycat
When is a fuse not really a fuse?
Replies
12
Views
289
audiodummy
audiodummy
I
I got half a deal today................
Replies
5
Views
603
jhal
jhal
Back
Top Bottom